Study of the role of nitric oxide (NO) in humans under physiologic and pathophysiologic conditions has been hampered by the lack of reliable measurement tools to determine changes in NO in plasma and tissue samples. This project utilizes a novel instrumentation system capable of analyzing all forms of NO in plasma and red cells. The overall objective of these studies is to apply NO measurement technology to determine circulating NO levels and distribution within the blood compartment during changes in vascular resistance in the peripheral and renal circulations in humans.